Method of recovering well fluids and conserving reservoir pressure



Sept. 26, 1939. J, WALKER'ET AL METHOD OF RECOVERING WELL FLUIDS AND CONSERVING RESERVOIR PRESSURE Filed Jan. 23, 1959 Patented Sept. 26, 1939 METHOD OF RECOVERING WELL FLUIDS AND CONSERVING RESERVOIR PRES- SURE JayP. Walker, Tulsa, Okla., and Edwin V. Foran,

San Antonio, rllex.,

assignors to Eureka Process Company, Tulsa, Okla., a corporation of Dela- Waffe Application January 23, 1939, Serial No. 252,380

9 Claims.

This invention relates to new and useful improvements in methods of. recovering well fluids and conserving reservoir pressures.

The invention has particularly to do with the recovery of certain hydrocarbon liquids, which so far as is known, occur in solution with natural gas in sub-surface reservoirs at relatively high temperatures and at high pressures within the retrograde condensation range, or above the l0 same, of the order set forth in our Patent No.

2,080,351, issued May 11, 1937, and in our copending application Serial No. 141,326, filed May 7, 1937, of which this application is a continuation in part. As pointed out in our preceding applications these wells are now generally known as distillate wells.

In the reservoirs to which this method relates, the natural gas as before stated occurs at relatively high temperatures, usually above 100 F.

and at high pressures usually above 1,000 pounds per square inch. Such gas contains desirable liqueable constituents, which when recovered are suitable for motor fuel and kindred purposes and are sometimes referred to as gasoline. These liqueable fractions or constituents exist in a highly dispersed vapor phase and remain in solution with the gas so long as the pressure is high enough. Whenever the pressure is reduced below the dew point of these gaseous reservoir products, within the retrograde condensation range of pressure, some of these liqueiiable constituents will condense and precipitate. Such a condition causes these condensates to wet the face of the sands in the reservoir, thus becoming substantially unrecoverable. From this it follows `that if, gas was being taken from the reservoir, as through an output flowing well, the reservoir products would be conserved, or at least better conserved, if a high reservoir pressure was maintained and the liqueable constituents would remain in solution with the gas, and thus be recoverable so long as the reservoir pressure was maintained above the dew point at which precipitation or condensation occurs.

One of the objects of the invention is to provide an improved method of recovering liquefiable hydrocarbons from gaseous sub-surface reservoirs of the type now commonly known as dis tillate, wherein the denuded gas is separated from the recovered liquids at high pressures, and returned to a gaseous or distillate sub-surface reservoir for the purpose of maintaining such high pressures therein as to prevent condensation and precipitation of desirable liqueable components, and their absorption by the reSCrvoir CFI sands, which would occur, due to the retrograde condensation phenomena, if the pressures in such reservoirs were allowed to drop as the gas was produced therefrom through one or more out-put wells.

Another object of the invention is to provide a method of the character described wherein the denuded gas is separated or recovered at such high pressure that it may be returned to the subsurface reservoir either without compression or with such little compression as to make for low compression costs.

An important object of the invention is to provide a method, dealing particularly with subsurface reservoirs of the type described, in which desirable hydrocarbon liquids are found in gaseous form in natural gas, which greatly predominates in the reservoir, and is under high pressure within the retrograde condensation range, whereby the desirable liquids and gases are recovered by processing the gas within the retrograde condensation range; and also whereby the high pressure gas is returned to a sub-surface reservoir to maintain a high pressure therein and prevent, or delay, precipitation or condensation of the desirable liquefiable constituents in such reservoir, which precipitation or condensation is usually due to pressure decline in the reservoir.

A particular object of the invention is to return the denuded gas recovered in a method of the character described, and at a high pressure within the retrograde condensation range, to the reservoir of the output Well as such a remote point as to move the natural gas in said reservoir toward an output well, and especially to move such gas en masse toward an output well, while maintaining a high pressure in the reservoir at a degree above the point at which appreciable precipitation or condensation of the desirable liqueable constituents takes place. An advantage of such a method is that substantially the entire volume of gas located between an output well and the remote input well may be processed in a single cycle of displacement or pressure decline, the input high pressure gas acting as a pressure medium in forcing the unprocessed gas ahead of it toward an output well in its own effort to move toward such output well.

A very important object of the invention 1s to provide a method of, the character described wherein the high pressure denuded gas is returned to the reservoir at such a remote point as to prevent contamination of the rich gas in the reservoir which is discharged through an output Well, so that when the denuded gas which is re- Still another object of the invention is to provide a method wherein the recovery of liquids is carried out at a high pressure, within the retrograde condensation range, and at least higher than which has been heretofore termed high pressure, as the term is commonly used in absorption and gasoline plants. By operating at such a high pressure the residual or denuded gas may be separated from the recovered liquids at such a high pressure as to make for economical compression, where compression is required. The particular pressure at which the retrograde condensation range begins is somewhat controlled by the composition of the liquids in solution with the natural gas. While some liquid components may go into solution with the gas at pressures as low as 650-pounds, other liquid components will not vaporize until a much higher pressure is reached. When handling one particular natural gas the retrograde condensation pressure range with respect thereto may begin at 650 or '700 pounds, while with another natural gas the retrograde range may not begin until 800 or 1,000 pounds, or even higher, are reached. At this time it would be diiiicult to limit the maximum pressure of the retrograde condensation range. It is a well established fact that several more stages of compression are required to raise a pressure from pounds to 1,000 pounds than is necessary to raise a pressure from 1,000 pounds to 2,000 pounds. The cost of compression is high and the revenue received from the sale of the recovered liquids would not be suillcient to return a profit if several stages of compression were required in order to return the gas to a sub-surface reservoir. The method herein set forth contemplates recovering the denuded gas at such a high pressure that it may be returned to a high pressure reservoir, within the retrograde condensation range, with a single stage of compression, although under some circumstances or conditions more than one stage may be necessary.

The method involves returning the gas to the sub-surface reservoir of an output well, as well as to another sub-surface reservoir. In returning the gas to another or independent subsurface reservoir the step maybe carried out Without recompressing because of the very high pressure at which the denuded gas is recovered, or the denuded gas may be recompressed. It is not the purpose of the invention to admix the denuded gas with the rich gas which is being processed for the recovery of desirable liqueiiable constituents, but on the other hand it is an object of the invention to prevent as far as possible contaminating the rich gas with the denuded gas to the end that when the input denuded gas reaches the output well the recovery of liqueable constituents from the rich reservoir gas will have been completed and the recovery method will have gone its limit.

Apparatus capable of carrying out the method of the invention will be hereinafter described, together with other features of the invention.

The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawing in which diagrammatical illustrations of apparatus for carrying out the method are shown, and wherein:

Figure l is a diagrammatical view illustrating earth formations of widely separated output and input wells with apparatus for carrying out the method located therebetween,

Figure 2 is a plan view in diagram form of the apparatus located on the surface.

In the drawing, the letter A designates a well of the distillate type flowing under pressure and B the high pressure sub-surface reservoir thereof producing gaseous fluids or natural gas having liqueilable constituents in solution therein. In such reservoirs, the gas is under high pressure within the retrograde condensation range and the temperature is higher than in the reservoirs of more shallow wells, consequently the well head pressure is generally comparatively high. At a rule these wells produce little or no crude oil or heavy hydrocarbon oils; however, reservoirs may be encountered which will produce some heavy hydrocarbon oil as well as natural gas at pressures within the retrograde range of condensation. While the limits have not been established, the temperatures which have been ascertained are above 100 F., some of the wells flowing at a well head temperature of 120 F. and higher. Reservoir pressures may range from 1,000 pounds to 3,000 pounds pressure, but usually the reservoir pressure is above 1,500 pounds and may go much higher than 3,000 or 4,000 pounds.

The letter C designates an input well and D the sub surface reservoir thereof, which may be a remote portion of the reservoir B or a separate gaseous reservoir. It must be clearly understood that in order to carry out the invention, the wells A and C must be separated a considerable distance when they are both drilled into the same reservoir. While this distance cannot be iixed, it should be suilicient to accomplish the purposes sought and such distance will, of course, be limited somewhat by the extent of the pool or the lease which is being operated. It is contemplated that these wells may be separated anywhere from one-half a mile to two or three miles, but these measurements are not to be taken as limitations. The method has been in operation for more than a year in a gas field in southern Texas, where the input well is located approximately a mile and a half from the output well. So far there has not been the slightest trace of denuded gas in the rich natural gas flowing from the Youtput well and the well head pressure is still high in the retrograde condensation range. Where the high pressure gas is delivered to another reservoir distance between reservoirs or wells, of course, is not an important factor, but high pressure is.

It has, of course, been the practice to introduce gas into sub-surface reservoirs but more frequently the purpose has. been to repressure a de pleted or partially depleted oil reservoir. Such methods involve the use of the gas to pick up desirable liquids remaining in the reservoir after primaryvdepletion has taken place. Many of the methods include introducing extraneous or foreign fluids such as water and engine gases as wellas heavy oils and air. In substantially all of these methods there is an admixture of the input gas with the flowing gas so that the iiowing gas is contaminated and either diluted or deteriorated. Such a procedure in the present method would be fatal to its successful operation. In carrying out our method, as illustrated in Figure 1, we do not in returning the residual gas to the reservoir, employ any of these other methods, nor do we attempt to accomplish any of their results. This is largely due to the fact that the inherent nature of the'products in the reservoir to which our method is applied is so totally diiferent from the products in the reservoir to which the other methods are applied. So far as we are aware, no one has ever attempted to process natural gas containing liqueflable constituents in solution at such a high pressure that the liquids could be recovered and the gas sepa,

rated at such a high pressure as to return it to the reservoir either under such high pressure or with economic recompression; and particularly to employ such returned high pressure gas to conserve the reservoir pressure and displace the gas therein according to the teachings of this invention.

Again referring to the drawing, the letter E designates a pipe for conducting the stream of rich natural gas from the well A and this pipe may includea choke or regulating valve E. It may be desirable to reduce the flowing pressure at this point. As an illustration, where the well head pressure is around 3,000 pounds, it may be desirable to reduce the pressure through the choke E to around 2,000 pounds. Such reduction would, of course, be within the retrograde condensation range and would enable the method to be carried out at a lower flowing pressure without sacrificing any of the advantages. Such a pressure reduction would aid to some extent in reducing the temperature and also in causing condensation of liquefiable fractions, however, it would not be suilicient for the purposes of this method. It would be possible to reduce the pressure through the choke E' sufficiently to cause profitable cooling and condensing and the inven tion is not to be limited to any particular pressure reduction through the choke E. The pipe E conducts the gas stream, which is flowing under high pressure, into a tank F which may be called a mixing tank or, as in our Letters Patent, it may be referred to as a liquedenser. This tank may be of any suitable construction but is preferably provided with battles or other elements, common in this art, for causing a thorough admixing of liquids or fluids flowing through the tank.

A pipe G leads into the lower portion of the tank F for the purpose of introducing a liquefaction or agglomerating liquid. This liquid may have substantially the same composition as some of the natural liquids which are in solution with the natural gas and are to be recovered therefrom. In some of the plants which are in use, liquids recovered under this method are generally classified as motor fuels, although they may include substantial amounts of kerosene and heavier hydrocarbons. Owing to the composition of the liqueable fractions in solution in the natural gas in the type of reservoirs to which this method relates, the recovered liquids will always be more or less of gasoline content. Such components as propanes, butanes, pentanes and heavier derivatives will be recovered under this method. As will be hereinafter pointed out, the mixing of the natural gas and the liquefaction liquid should occur at a reduced temperature. Where the gas discharges from the well at temperatures ranging from to 120 F., it has been found profitable to reduce the temperature of the admixture in the tank F to as low as 40 F. It is obvious that either the liquefaction liquid itself may be cooled low enough to produce such a temperature, and this is the preferable procedure, or cooling may be brought about in any other suitable manner.

The natural gas which is discharged into the 5 tank F from the pipe E admixes with the liquefaction liquid which is discharged into said tank from the pipe G. These fluids and liquids flow concurrently and upwardly through the tank which is, ,of course, filled therewith while the 10 method is in operation. In flowing through the baffles or other mixing elements of the tank a thorough admixture is carried out. The details of one method of admixing the well fluids is set forth in our aforesaid patent and it is not be- 15 lieved necessary `to describe this method in detail in this specification. However, when a method is used which involves the introduction of a liquefaction liquid, it has been found that the best results are had where the liquefaction liquid is 20 cooled sufficiently to produce the proper temperature in the mixing tank. Very good results have been had where the temperature in the mixing tank is between 35 and 50 F. but this temperature is subject to variation both upwardly and 25 downwardly. It may be necessary to cool the liquefaction liquid to a lower degree than the degree of admixture. The invention is not to be limited to any particular temperature. The stream flowing through the pipe E is, of course, 30 gaseous and is commonly referred to as natural gas. While the invention is not to be specifically limited, it has been demonstrated that in the majority of cases the liquefaction liquid should be introduced in generous quantities, and some- 35 times in quantities greatly in excess of the liquid content of the gas, and thus produce in the admixtul'e a total liquid content either `in excess or greatly in excess of the normal amount of the natural liquefiable content of the well stream.

As pointed out in our patent hereinbefore referred to, the admixing of the liquefaction liquid together with the reduction in temperature causes condensation or precipitation of the liqueable constituents entrained in the gas. In addition, 4l the introduction of the liquid causes agglomeration of liquids of like composition and thereby increased recovery is effected. It is most desirable not to reduce the pressure below the retrograde condensation range although the temperature is 50 greatly reduced. The admixture of liquids and fluids which flows upwardly in the tank F is discharged from the top thereof through a pipe H which leads to a high pressure separator I of suitable construction. As hereinafter set forth, 55 this separator is provided with regulating valves to maintain a predetermined pressure therein. The admixing of the liquefactionv liquid with the gas will not only occur in the tank F but will continue while the stream is flowing through the 60 pipe H, so that when said stream reaches the separator I, it will be prepared for separation. When the stream enters the separator I, the gas will readily separate from the liquids. It is preferable to use a separator which is designed to 65 thoroughly separate all of the liquids from the gas so that denuded gas may be discharged as such from the top of the separator through the pipe O. The liquids will, of course, accumulate in the lower portion of the separator and such 70 liquids will include those which are condensed or* recovered from the natural gas as well as .the liquefaction liquid introduced through the pipe G.

It may be desirable and is common practice to provide the separator I with a pressure reduc- 'I5 tion valve H which may be in the form of a choke. This choke may be set to reduce the pressure of the admixed stream just prior to its discharge into t'he separator but such reduction will still maintain the pressure in the separator within the retrograde condensation range or substantially so. As an illustration, the well head pressure of the well A may be 3,000 pounds and the choke E may be set to reduce it to 2,000 pounds. In such instance the choke H may be set to reduce the pressure to 1,100 pounds and this would enable the gas to be discharged into the pipe O at well above 1,000 pounds.

A pipe J extends from the lower portion of the high pressure separator for carrying o3 recovered liquids for sale, for use, or for other disposition. This pipe includes a suitable discharge valve. Ai pipe K extends from the bottom of the separator for carrying off quantities of the recovered liquids to be used as a liquefaction liquid. This pipe is preferably connected with a cooler L for carrying out a heat exchange to reduce this reflux or recirculated liquid to the proper low temperature. Water, ammonia, or any other cooling medium may be used in the cooler. A discharge pipe M carries the reflux liquid to a pump N to which the pipe G is connected. By this arrangement, recycling of the recovered liquids as the liquefaction liquid is accomplished.

The invention is not to be limited to the recovery of liqueflable hydrocarbon constituents by admixing a reflux liquid therewith. It has been demonstratedthat liqueiiable constituents in solution in natural gas in the pressure range of retrograde condensation may be recovered by three modes. Recovery may be made by reducing the pressure and coniining the reduction within said retrograde condensation range; by cooling the gas sufficiently to cause condensation of said constituents, while maintaining the pressure within said retrograde range; or by adrnixing with the natural gas a liquefaction liquid at such a low temperature as to bring about agglomeration and condensation. This invention is not to be so limited as it contemplates the use of any of these three steps; its essential being that the method must be carried out at such a high pressure that the residual and denuded gas will be recovered so that it can be introduced into a subsurface reservoir at a high pressure either with or without compression, the pressure of the recovered gas being within the retrograde condensation range or substantially so that it may be recompressed economically.

As before explained, the pipe O leads from the top of the separator I for carrying oil' the residual gas. 'Ihe pressure diil'erentials between the owing pressure at the well head and the pressure of the gas discharged into the pipe O will depend largely upon particular reservoirs and the conditions under which the method is performed. Irrespective of the well head pressure, the pressure of the denuded gas discharged into the pipe O will always be high and preferably within the retrograde condensation range. As before indicated, the term "high pressure as usually employed in gas processing refers to a pressure of 200 to 300 pounds, but the term as used herein refers to much higher pressures, which would be considered abnormally high in referring to pressures in gas processing. While it is preferable and highly desirable to limit the reduction of the gas pressure within the retrograde condensation range, there may be instances, owing to the composition of the liquids, in which the lower limit of the retrograde range will be higher than the range of other compositions. For instance, where the retrograde range would begin at 650 pounds or 700 pounds pressure with respect to one composition, the range may not begin until 1,000 pounds is reached with respect to another composition. The components of the liquids will vary according to different reservoirs and this will be true not only of quality but of quantity. From the foregoing, it is apparent that if the pressure was reduced to 800 pounds, it would be within the retrograde condensation range of one composition of liqueable fractions, but it might be below the retrograde condensation range of another composition, therefore, the term substantially is employed as related to the lower limits of the retrograde condensation range. It might be stated that in most instances the pressure at which the denuded gas is separated will be within the retrograde condensation range.

In carrying out the surface steps of the method,

gas may be separated at 1,000 pounds or at 1,500 pounds or even at 2,000 pounds or at any other satisfactory high pressure. The well head pressure may be very much higher than 3,000 pounds or it may be lower. The method steps may include one or more pressure reductions before the reservoir pressure, or recompression.

It is well known each compressor handling the same volume of free gas or since the gas from the point of ilnal separation may be delivered to the compressor under a comparatively high pressure, the said compressor necessary in raising the gas prespressure were delivered to said compressor. 'Ihis results in a reduction of compressor equipment ef such magnitude that it becomes economical to introduce the separated gas into the formations. 'Ihis is an important feature of the invention because, heretofore, it has not been practical to return gas to reservoirs of this type because the cost of equiping, maintaining and operating the compressors to raise the gas to a necessary pressure, was prohibitive.

'I'he products recovered in separator I include residual gas, usuallv at a high pressure. and llq air per minute. It follows then that put it back in the formation. A pipe Q leads from the compressor to the input well C.

For the purpose of utilizing the denuded gas without recompression, a pipe R is shown extending from the pipe O and including a valve S. The pipe R may be connected to an input well, whereby the residual gas may be returned to a sub-surface reservoir without raising its pressure. Such a sub-surface reservoir may be at another elevation in the same eld as the well A or it may be in another structure or pool.

Where the denuded or residual gas is returned to the same reservoir from which the rich gas was discharged, it is desirable, as hereinbefore set forth, that such separated gas be returned to the reservoir at a point which is substantially remote from the output Well that it will not contaminate the outowing gas, and also that it will act as a pressure medium. It becomes obvious that the method of Vthis invention requires a particular type of reservoir, and so far as its function as a pressure medium is concerned, the reservoir must be predominately gaseous and there must be liqueable hydrocarbon constit uents in solution in such gas. It is not the purpose of this invention to apply the method to an ordinary oil and gas reservoir such as the usual oil well produces from, or to a gas reservoir which does not contain liqueable hydrocarbon constituents at temperatures and pressures Within the retrograde range phenomena, button the contrary it is the purpose to return the denuded gas to a particular type of reservoir wherein the desirable components are found and it is sought to maintain the high pressurey within the retrograde range within such reservoirs, which are known as distillate or condensation wells. The sand in the gaseous stratum of these distillate type of reservoirs, is in the ordinary sense of the word, dry, due to the high temperature and high pressure; however, the gas is laden with liqueflable constituents of varyingl compositions which would condense, be adsorbed in this dry sand, and be lost so far as recovery is concerned, if the reservoir pressure is permitted to drop.

If the gas is returned to its original reservoir, the importance of locating the input well at a considerable distance from the output well cannot be too greatly stressed. The theory, and such theory is believed to be sound, is that by returning the denuded gas to the reservoir at a remote point, and at a high pressure, not only will the yhigh pressure in the reservoir be conserved, but the rich gas therein will be displaced en masse toward the output well. While there will be some contamination of the rich gas in the immediate zone of contact between the input gas and the reservoir gas, there will not be any tendency on the part of the denuded gas to channel through the reservoir gas or pass over it, on account of the fact that the denuded gas and the reservoir gas are a one phase product, and not a two phase product as in an oil and gas well. Furthermore, the input gas in flowing through the reservoir toward the output well will sweep the rich reservoir gas before it so that when such input gas does reach the output well, substantially all of the reservoir gas in its path will have been discharged through the output well.

Although the reservoir contents of the distillate type of pool may al1 be in the gas phase at the time of discovery, they do not long remain so if,l during development, an appreciable decline in reservoir pressure takes place. of the heavier hydrocarbon vapors will condense 'or precipitate in the reservoir as the pressure is lowered, even though no change in temperature takes place. This phenomenon is known as retrograde pressure condensation. In this respect the deep high-pressure .reservoirs oi wet gas react to pressure decline in a manner exactly opposite to that of the shallower or ,low pressure wet-gas reservoirs whose contents are composed of morevvolatile contents than the deep pools.

From the foregoing it is obvious that by returning the 'gas to the original reservoir at a remote point the rich reservoir gas will be displaced or discharged through the output well in a single cycle of operation. While there will be a slight decline in the reservoir pressure, such pressure decline will not result in appreciable precipitation or condensation, due to the return of the major portion of the gas to the same reservoir. Unquestionably, the I nethod will greatly prolong the protable life of the reservoir as well as preventing a pressure decline to the point where the liqueable constituents would condense or precipitate in substantial quantities, and become absorbed in the sands, thereby becoming substantially unrecoverable, as would be the case were the gas not to be returned to the reservoir or the reservoir pressure not conserved.

It has been definitely demonstrated in the processing of natural gas of the character involved herein, that cooling the gas is of great importance. Further, it has been shown that cooling alone is suiiicient to condense liqueiiable constituents. Such cooling may be acquired by various steps as has hereinbefore been pointed out. In actual practice, cooling has been effected by reducing the pressure to a proper degree in. the retrograde condensation range, as well as by applying an exterior cooling means such as ice, ammonia or cooling liquids or uids. In the particular apparatus illustrated in the drawing,` all of applicants cooling is provided by reducing the temperature of the reflux liquid to the desired low temperature to produce suicient cooling when the reux is admixed with the gas. So far as the invention is concerned, it is immaterial as to just how the cooling Vof the gas is obtained.

The term distillate, as used herein, refers Some" to hydrocarbon components Which are produced .temperature has generally been from F. up-

wardly. Reservoir pressures of several thousand pounds have been encountered. When the pressure is reduced within this range these vapor phase or gaseous hydrocarbon components are liqueed and this occurs without reducing the temperature; From this it becomes quite obvious that if the pressure in this type of reservoir was reduced from 2,000 pounds to 1,500 pounds, even grade condensation range which includes, iiowing the gas from the well under high pressure within said retrograde condensation range, cooling the gas vwhile maintaining the pressure substantially within the retrograde condensation range to condense liqueable hydrocarbon constituents, separating the gas from the liquids at a high pressure substantially within the retrograde condensation range. raising the pressure of the high pressure denuded gas only suiilcient- 1y to return it to a high pressure gaseous reservoir, and returning the repressured gas to a gaseous reservoir through an input well and employing said returned gas to displace the gaseous products in said reservoir en masse toward the output well for prolonging high reservoir pressures.

2. The method of recovering desirable liqueiiable constituents from a gaseous reservoir which is initially Aat a high pressure within the retrograde condensation range of said constituents in the reservoir which includes, conducting the gas from the well at a high pressure within the retrograde condensation range, flowing said gas in heat exchange relation with a cold fluid at high pressure within said retrograde condensation range to lower the temperature offsaid gas and to condense said constituents, separating the resulting condensed constituents from uncondensed gas, raising the pressure of the uncondensed gas only sufficiently to return it to the reservoir through an input well located at a remote point from the output well, and employing said returned gas to displace the gas in said reservoir of the character described en masse toward the output well for prolonging high reservoir pressure.

3. The method of recovering liqueable hydrocarbon constituents from a gaseous reservoir in which lthey are in solution with natural gas and are under high pressure within the retro- `grade condensation range winch includes, conducting the well stream containing said liquefiable constituents from an output well under high pressure, flowing the well stream and admixing therewith a cooling and agglomerating medium of kindred characteristics to the liquids to be recovered from the said stream while maintaining the admixture within the pressure range of retrograde condensation, whereby the liqueiiable constituents are condensed in said stream, separating the residual gas from the liquids at a high pressure substantially within the retrograde range, and introducing the high pressure residual gas to a gaseous sub-surface reservoir for maintaining high gas pressure and minimizing retrograde condensation in said reservoir into which said residual gas is introduced.

4. The method of recovering liquefiable'hydrocarbon constituents from a gaseous reservoir in which they are in solution with natural gas and are under high pressure 'within the retrograde condensation range which includes, ilowing the gas from the reservoir through an output well under high pressure within said retrograde condensation range, cooling the gas while maintaining the pressure substantially within the retrograde condensation range to condense liqueiiable hydrocarbon constituents, separating the gas from the liquids at a high pressure substantially within the retrograde condensation range, raising the pressure of the high pressure denuded gas only sumciently to return it to the said high pressure reservoir, and returning the repressured gas to the gaseous reservoir through an input well located at a remote point from the output well and employing 'said returned gas to displace the gaseous products in said reservoir en masse toward the output well for prolonging high reservoir pressures, whereby said liqueiiable hydrocarbon constituents may be recovered from said reservoir during a. single cycle of pressure decline in said reservoir.

5. The method of recovering gaseous products from Wells producing such products in gaseous form which includes, conducting the well stream containing said products from a well under pressure, admixing with the gaseous fluids of the well stream a liquefaction liquid having components of kindred characteristics to the liquids to be recovered from said well stream, whereby liquefiable components of the well stream are precipitated and agglomerated with the liquefaction liquid and form the final liquid to be recovered, separating the gas from the agglomerated stream, carrying out the preceding steps at a minimum reduction in pressure, raising the pressure of the residual gas, and returning the residual gas to the sub-surface reservoir of the output well through an input well located at a remote point from the output well and employing it to` displace the gaseous products en masse toward the output Well for maintaining high reservoir pressures and decreasing precipitation of liqueable hydrocarbons into the sands.

6. The method of recovering liquei'lable hydrocarbon constituents from the reservoirs of distillate type of wells which includes, ilowing the gas under high pressure from the reservoir to the surface of the ground throughv an output `well, reducing the pressure and cooling the flowing gas only. suiiiciently to condense and recover liquefiable hydrocarbon components therefrom, separating denuded gas from the liquids at a high pressure, and returning the high pressure gas to a distillate type reservoir through an input well to maintain high gas pressure in said reservoir and minimize condensation and precipitation of liquefiable components in said reservoir due to retrograde condensation.

7. The method of recovering liqueiiable hydrocarbon constituents from the reservoirs of distillate type of v[wells which includes, flowing the gas under high pressure from the reservoir to the surface of the ground through an output Well, reducing the pressure and cooling the flowing gas only suiiciently to condense'and recoverl liqueable hydrocarbon components therefrom, separating denuded gas from the liquids at a high pressure, returning the high pressure gas to its original reservoir through an input welltomaintain high gas pressure in said reservoir and minimize condensation and precipitation of liquefiable components in said reservoir due to retrograde condensation, and displacing the gaseous products in the reservoir en masse from the input well toward the output well by the high pressure gas returned to the reservoir.

8. 'I'he method of recovering liqueiiable hydrocarbon constituents from the reservoirs of distillate type of wells which includes, flowing the gas under high pressure from the reservoir to the surface of the ground through an output well, reducing the pressure and cooling the flowing gas only suciently to condense and recover liqueable hydrocarbon components therefrom, separating denuded gas from the liquids at a high pressure, returning the high pressure gas to the same reservoir through an input well 1ocated at a remote point from the output Well and employing said returned high pressure gas to maintain a high gas pressure in said reservoir to prevent condensation and precipitation of liqueable components in said reservoir and also to displace the unprocessed gas in said reservoir en masse toward the output well.

9. The method of recovering liqueable hydrocarbon constituents from the reservoirs of distillate of Wells which includes, flowing the gas under high pressure from the reservoir to the surface of the ground through an output well, reducing the pressure and cooling the nowing gas only suiciently to condense and recover liqueflable hydrocarbon components therefrom, separating denuded gas from the recovered liquids while maintaining said gas at such a high pressure as to require only minimum compression to return it to the high pressure reservoir from which it was produced, compressing the separated gas to raise its pressure only suiicient 1y to return it to said reservoir, and returning the compressed gas to the'said reservoir through an input well and employing said returned high pressure gas to maintain high reservoir pressures for minimizing retrograde condensation and to displace the unproduced gas in said reservoir en masse toward the output well, whereby said liqquefable hydrocarbon constituents may be recovered from said reservoir during a single cycle of pressure decline therein.

JAY P. WALKER. EDWIN V. FORAN. 

